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Colloidal Solution

True Solution, Suspension and Colloidal Solution

Based on distinct properties, solutions can be classified into True Solution, Suspension and Colloid. This classification is necessary to understand concepts of colloidal solutions and distinguish it from rest of the types.

True Solution

True Solution is a homogeneous mixture of two or more substances in which substance dissolved (solute) in solvent has the particle size of less than 10-9 m or 1 nm. Simple solution of sugar in water is an example of true solution. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye.

Suspensions

Suspension is a heterogeneous mixture in which particle size of one or more components is greater than 1000nm.When mud is dissolved in water and stirred vigorously, particles of mud are distributed evenly in water. After some time, the particles of this solution settle under water due to influence of gravity. This solution is an example of Suspension (see picture below). Contrary to True Solution,particles of suspension are big enough to be seen with naked eye.

Suspension Settled Muddy Water

Suspension Settled Muddy Water

Colloidal Solution

Colloidal Solution is a heterogeneous mixture in which particle size of substance is intermediate of true solution and suspension i.e. between 1-1000 nm. Smoke from a fire is example of colloidal system in which tiny particles of solid float in air. Just like true solutions, Colloidal particles are small enough and cannot be seen through naked eye.They easily pass through filter paper. But colloidal particles are big enough to be blocked by parchment paper or animal membrane.

Black Cloud of Smoke with Fire in Forest

Black Cloud of Smoke with Fire in Forest

Difference between True Solution, Suspension and Colloidal Solution

The table given below summarizes the major properties and points of distinction between each type of solution with respect to different properties.


Property True Solution Colloidal Solutions Suspension

Size of the particles < 1nm 1– 1000nm >1000nm

Nature Homogeneous Heterogeneous Heterogeneous

Filterability(Diffusion through parchment paper) Particles of true Solution diffuse rapidly through filter paper as well as parchment paper. Colloidal particles pass through filter paper but not through parchment paper. Suspension particles do not pass through filter paper and parchment paper.

Visibility Particles of True Solution are not visible to naked eye. Colloidal particles are not seen to naked eye but can be studied through ultra microscope. Suspension particles are big enough to be seen by naked eye.

Tyndall effect True Solution does not show Tyndall effect. Colloids shows Tyndall effect. Suspension may or may not show Tyndall effect.

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